First off, what Hammerfight is:
Hammerfight is a physics-based game made by Konstantin Koshutin where you play as a small "helicopter", the goal is to defeat your enemies. It's set in a steam-punk-esque universe.
But, it's radically different from other fighting games, and here is why:
In Hammerfight you don't mash a "attack button", you use physics to inflict damage. The best way to explain how this works is through the trailer:

The weapons range from heavy steel wrecking balls to small and agile swords, from guns to thrown spears and poison flasks. Most weapons can also be improved by adding a gem, gems can change a lot in a battle, from a simple damaging gem to a "ghost gem" that allows you and your weapon to go through solid objects for a short moment (great against shields).
Your fighting style will change radically with each weapon, trying to use a sword the same way you used a flail isn't possible (since they deal damage in completely different ways).

The environments are nearly completely destructible, you can hit your enemy and send him flying into the wall, and sometimes trough it. If you see something that looks like it can be broken, chances are it can, if it looks like it can be lit on fire, it probably can.
Is your enemy too agile and you can't hit him with your huge demolition ball? Smash the roof and shower him with bricks, stones and various heavy objects (when you smash something, the debris does not disappear, so if you are good enough you could send falling stones flying towards your enemy by hitting them with your weapon).

The art style is pretty unique, it borrows a bit from the middle-eastern culture and a bit from the steam-punk style, and some locations are gorgeous even though the game is only in 2D. The decorations and effects are great too, and give a great atmosphere to the fights.

At the moment, only hotseat multiplayer battles are possible (for which you will need two mice), and while there are rumours about a multiplayer patch, most of those I have read are translated from Russian, so I can't say if it is planned or how long it will take for it to be released.
That said hotseat multiplayer games are extremely rare on the PC (even more so if the game is in real time and not turnbased), and being able to call over a friend and play on the same computer without having to buy another copy of the game is a nice change from all the usual industry standards.

Basic Fighting Tips, read this
[release]Basics:
-Blunt works best against armour (other armoured helicopters), edged works best against unarmoured (worms and beasts).
-Moving the mouse quickly from side to side taunts enemies, spurring them into attacking (they go pretty berserk, so be careful)

Swords: Swords are, usually, light but sharp weapons. As such they should not rely on momentum to cause damage. When you hit an enemy you don't want the central mass to hit the enemy and stop, what you want is the blade to slide on the enemy at highest possible velocity. Best way to do this is to either hit the enemy while pulling back (weapon hits, then slides) or hitting with the top 25% of the weapon (if the blade is curved). You can also stab with swords.
Swords are possibly the hardest to use, but also the most precise (when you are good with them, you can easily slice of the head of an explosive wasp, while leaving the volatile body intact).

Flails/Maces/Balls: The easiest weapons to use, but you still can't just make circles and expect to win. When you are not attacking don't swing madly, because that momentum you are building up will make it hard to aim (also you might en up being the one swinging around, if you aren't careful). One or two slow full rotations right before the swing can help adding some extra punch, but you will have to swing when the weapon is in the right place, otherwise that momentum will ruin your swing. With these weapons be sure not to overdo the swing and lose control, slamming into a wall when 2 other jackasses are hammering you usually means death.
Hit enemies in full force, send them flying then smash them when they are stunned. Also usually they have the longest reach, so it becomes easier to hit a downed enemy without slamming into the ground.

Hammers: Like flails, only with a rigid handle. Work similarly but are usually more controllable.

Axes: Cross between swords and flails, some can be used similarly to a sword, but usually they work more or less like hammers, with the added sharpness. Some axes have more/longer blade, they can be used more like sword, with sliding blows.

Gems:
You can get gems throughout the storyline or by completing Grim.

Topaz: Lights enemies and the environment on fire.
Sapphire: Freezes parts of the environment, weapons and armour. Also frozen enemies take more damage.
Ruby: Heals you on hitting an enemy.
Amethyst: Creates arcs of electricity and shocks enemies.
Emerald: Makes you noclip for a small amount of time, allowing you to go through things (like that thrown hammer coming at your face at warp-speed).

Sockets:
Small sockets: Can hold one small gem
Large Socket: Can hold one large gem
Golden Socket: Can hold either one large gem or one small gem (I've never seen a Gigantic gem drop, so at the moment the only possible way to acquire one at the moment is file editing)

Even though Hammerfight is a 2D game, you may want to be careful if you are going to buy it to be played on an old machine, I have tried it on a Intel integrated GMA950 and while it was playable, it was considerably slower than normal (felt like slow motion), but I'm quite sure that quite a few frames per second could be gained by tweaking the configuration.

Some tweaking:

Code:

You may want to tweak some stuff, to do that go into your X:\Steam\steamapps\common\hammerfight and open the Config.ini file.
Here you can set the resolution, various graphical settings and a lot of other stuff. You can (and possibly will) disable the trail behind the weapons for example (which should be GFX_RENDER_MOTION) or disable the "laughing"-thing (which should be GAME_JOKER)
GFX_MAXBURN and GFX_MAXMOVEABLE do what they state, set the maximum amount of moveable and burnable objects. Put it to something like 150 for some real mayhem (and epic fights in a burning arena).

You can also remove the time limit by setting it to -1 in a config. You don't have to delete the save every time. I just forget how to do it since I haven't played in forever.

Edit:

Nevermind I found how to remove the time limit.

Copy-Paste

another way (two ways, kinda) to get around the time limit:
(I like this way better, as it is less likely to cause problems, I think.)
when you are down to say, 30 minutes left, or 10, or 5, or whatever, go into the saves folder and open the profile you want to extend the time for. scroll down till you see the line that says 'm_roots=' followed by a number. this is where your time remaining is stored. replace the line with this:

m_roots=1.07412e+007

that should give you about 54 minutes remaining. when you're time gets low, just replace the line again.

alternatively, replace the line with

m_roots=-1

and you will have infinite time. I do not know how this will effect the game, it probably wont.
IMPORTANT: I am fairly sure that you will have to do this AFTER you do the first two levels, the tutorialish ones. this is because you're time is set AFTER them. if there are any levels in the solo that dont count to your time, they may reset you're time so its not infinite any more... I am not sure. dont think that will happen, but if it does, just repaste the line.

It really makes me wonder where you're getting the BS about a 1.0 commercial release. He hasn't updated anything in more than a year.

This game isn't hard or confusing. You don't speak Russian and are using an English translation, you shouldn't be complaining about it being confusing. Learn Russian if you'd like it to make sense. It's only hard to most of you because you're used to playing easymode garbage.